The present invention relates to a compact zoom lens barrel.
A conventional zoom lens barrel comprises a zoom system, by which one focal length is switched to another focal length, and a focusing driving system, by which focusing is conducted. In conventional zoom lens barrels, several system, in which zooming and focusing are linked together, have been proposed.
For example, in Japanese Patent Publication Open to Public Inspection No. 287833/1988, and No. 248110/1991, the following has been proposed: a focal length switching cam portion and a focusing cam portion are linked together, and form one driving system; focal length switching and focusing are conducted by this one driving system, and a subsidiary optical system is not necessary. In these publications, a zooming region is divided into a focal length switching region and focusing region; a focal length is selected stepwise; when a parallel cam portion, which is not moved in the direction of an optical axis at the time of focusing, is provided, a lens group other than a focusing lens group is used for focal length switching and focusing; and a lens barrel is made to be small and the cost is lowered. In Japanese Patent Publication Open to Public Inspection No. 259210/1986, a whole lens system is protruded at the time of focusing, however, disadvantageous points, which will be described later, occur in the whole lens system protrusion.
In these conventional technologies, the effect of thinning the lens barrel is small, and when a zoom lens, in which sensitivity for errors in distance between lens groups (which will be described in detail later) is high, is used for focusing by the zoom lens barrel, there are many disadvantageous points to be solved, such as focusing accuracy. Further, focusing operations of respective lenses have not been disclosed.
Presently, a zoom type compact camera advances in the direction of down-sizing and thinning of the camera body, however there are many obstacles to this advancement. First of these is dimensions of the zoom lens. When too much thinning is attempted, an fb (flange back) becomes too short, an aperture of the final lens, which is closest to a film surface, becomes large, and a switching mechanism for panorama photographing can not be housed in the camera body. Further, when the aperture of the final lens becomes large, the diameter of the lens barrel becomes too large, so that the camera body itself tends to become larger. Due to the foregoing, the present inclination is as follows: when the total length of the lens is kept to a certain value, and the lens barrel is constructed in the manner of double-structure, the amount in which the lens can be driven is kept constant and the length of the lens barrel is shortened.
However, the diameter of the double-structured lens barrel is large, and although the effect of thinning the lens barrel is high, the effect is low for a decrease of the diameter of the lens barrel. Accordingly, in order to decrease the diameter of the lens barrel, the structure of a cam cylinder+a cam pin+a helicoid is changed to a structure of a double helicoid+an inner cam.
This is structured as follows: a front lens group portion is linearly driven through a helicoid of the cam cylinder which is rotated by a lens barrel driving motor; and a rear lens group portion is driven by an inner cam provided inside the cam cylinder. Since the cam portion is not exposed on the external visible surface, the diameter of the lens barrel can be made small since the cam cylinder can also be used for an external visible part, and it is not necessary to provide a separate driving gear to the metallic cam.
However, the diameter of the front lens group portion, in which a focusing mechanism is housed, is still large. When a 6V battery is changed to a 3V battery in order to make the camera more compact, a focusing motor and the like can be enlarged in order to obtain a higher output power.
Further, in the zoom lens, an FC adjustment in which both a telescopic lens and a wide lens focus on the same plane, and an ff adjustment, in which both lenses, having focused on the same plane, focus on a focal plane, are conducted. In the FC adjustment, a space for adjustment is necessary between a diaphragm and the front lens group, and positions of the diaphragm and lenses are changed depending on the adjustment, which leads to problems, causing the diameter of the front lens group portion to be large. In the ff adjustment, it is necessary that the whole lens barrel is moved, and it is necessary that large parts, which are appropriately strong for supporting the movement of the lens barrel, are provided on the lens barrel, so that the diameter of the lens barrel become larger.
The number of lenses is decreased at the sacrifice of the brightness (F-number) of the photographic lens, and the dimensions of the lens barrel is made to be compact, accompanied with requirements for compactness and low cost of the lens barrel. Accordingly, lens performance and the like are necessarily deteriorated. Part members of the lens barrel are made of plastic. Accordingly, the focusing performance, and resolving performance are necessarily sacrificed due to the dimensional accuracy, deformation, and the like. As described above, the structure of compact zoom-lens cameras has been changed many times for the purpose of compactness and low cost. However, the compactness has almost reached its limit, and lower cost can not be achieved without sacrificing specifications and performance.
The above-mentioned problems can be overcome by a zoom lens barrel according to the present invention, in which the zoom lens barrel is characterized in that: a zoom lens is switched to a plurality of focal lengths by a moving means by which a plurality of lens groups are moved in the direction of optical axis; after a desired focal length has been selected, a focusing operation is conducted by the moving means; at least two lens groups, which are moved for switching focal lengths, are moved while a distance between lens groups is being changed so that the focusing operation can be conducted.